1. Field of the Invention
The present invention relates generally to biological waste water treatment and, more particularly, to a biological waste water treating apparatus which can be operated stably and efficiently for a long period of time.
2. Description of the Prior Art
Hitherto, as an aeration type activated sludge treatment apparatus for industrial waste water, municipal waste water, etc., (hereafter, they are simply called "waste water" in this specification), a fixed bed system and a moving bed system have been employed. In such systems an aerobic condition or an aerobic condition and an anaerobic condition are utilized. However, since in these conventional systems, activated sludge deposits and accumulates in filter beds excessively when they are used for a long period of time, the contact effect between waste water treated and bioactive membrane is reduced to prolong a period of time required for finishing the treatment. Therefore, in order to remove the activated sludge thus accumulated, it is necessary to wash the filter beds, but that is inconvenient because the operation of the waste water treatment system must be stopped during washing. An attempt to wash the filter beds without stopping the waste treatment operation in a conventional system has been proposed, but when such a technique is put into practice, a large amount of activated sludge deposits in the treating tank and the recovery of the activated sludge from the tank for precipitation treatment is accompanied by a large amount of water to be treated, which results in the requirement of a large settling tank.